1. Technical Field
The invention relates to a frequency generating circuit, and particularly relates to a clock generating apparatus and a fractional frequency divider thereof.
2. Related Art
A clock generating apparatus can provide a clock signal complied with a rated frequency. The clock generating apparatus is configured with a frequency divider in internal thereof, so as to change a frequency of the clock signal output by the clock generating apparatus. In order to accurately adjust the frequency of the clock signal output by the clock generating apparatus, the frequency divider in the clock generating apparatus is required to have a fractional frequency dividing function. In a conventional design of the fractional frequency dividing function, a delta-sigma modulator of the frequency divider may cause a quantization error that cannot be ignored. The quantization error directly contributes to phase jitter of the output clock signal.